Photocatalysts have garnered significant attention not only for their potential use in the production of hydrogen and/or oxygen from water, but also in the treatment of waste materials and purification of air. Photocatalysts are frequently formed from semiconductors or from organometallic complexes, such as chlorophyll. Of the two, semiconductors are generally favored owing in part to their chemical stability, low cost of production, broad energy bandgaps, and the ease with which they can be handled.
Semiconductor photocatalysis is initiated by absorption of a photon of light having a wavelength of sufficient energy that is unique to the particular photocatalyst. Photon absorption creates separated electrons and holes across an energy bandgap. The strongly reducing electrons and the strongly oxidizing holes, generated by the optical excitation, can be coupled to reactions that can degrade environmental contaminants, split water for hydrogen production, and the like.